OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Offsetting of Assets
Gross Amounts of Recognized Assets, Subject to a master netting arrangement or similar arrangement	$ 441,393	$ 417,769
Gross Amounts of Recognized Assets, Not subject to a master netting arrangement or similar arrangement	130,543	124,474
Gross Amounts of Recognized Assets	571,936	542,243
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position, Subject to a master netting arrangement or similar arrangement	441,393	417,769
Net Amounts of Assets Presented in the Statement of Financial Position	571,936	542,243
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	211,435	171,384
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	102,913	100,890
Net Amount, Subject to a master netting arrangement or similar arrangement	127,045	145,495
Net Amount	257,588	269,969
Free-Standing derivatives
Offsetting of Assets
Gross Amounts of Recognized Assets, Subject to a master netting arrangement or similar arrangement	441,393	417,769
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position, Subject to a master netting arrangement or similar arrangement	441,393	417,769
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	211,435	171,384
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	102,913	100,890
Net Amount, Subject to a master netting arrangement or similar arrangement	127,045	145,495
Embedded derivative - Modco reinsurance treaties
Offsetting of Assets
Gross Amounts of Recognized Assets, Not subject to a master netting arrangement or similar arrangement	1,008	2,573
Embedded derivative - GLWB
Offsetting of Assets
Gross Amounts of Recognized Assets, Not subject to a master netting arrangement or similar arrangement	129,344	121,752
Other
Offsetting of Assets
Gross Amounts of Recognized Assets, Not subject to a master netting arrangement or similar arrangement	$ 191	$ 149